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After commit cc2c7d65fc27e877c9f407587b0b92d46cd6dd16 added this flag,
failure to reset it caused assertion failures. In non-assert builds, it
made the system fail to achieve the objectives listed in that commit;
chiefly, we might emit a spurious log message. Back-patch to v15, where
that commit first appeared.
Bharath Rupireddy and Kyotaro Horiguchi. Reviewed by Dilip Kumar,
Nathan Bossart and Michael Paquier. Reported by Dilip Kumar.
This commit has been applied as of b4f584f9d2a1 in v15 and newer
versions. This is required on stable branches of v13 and v14 to fix a
regression reported by Noah Misch, introduced by 1f95181b44c8, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints. The backpatched versions of
the patches have been aligned on these branches by me. Tests have been
conducted by the both of us.
Discussion: https://postgr.es/m/CAFiTN-sE3ry=ycMPVtC+Djw4Fd7gbUGVv_qqw6qfzp=JLvqT3g@mail.gmail.com
Discussion: https://postgr.es/m/20250306193013.36.nmisch@google.com
Backpatch-through: 13
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The previous commit addressed the chief consequences of a race condition
between InstallXLogFileSegment() and KeepFileRestoredFromArchive(). Fix
three lesser consequences. A spurious durable_rename_excl() LOG message
remained possible. KeepFileRestoredFromArchive() wasted the proceeds of
WAL recycling and preallocation. Finally, XLogFileInitInternal() could
return a descriptor for a file that KeepFileRestoredFromArchive() had
already unlinked. That felt like a recipe for future bugs.
This commit has been applied as of cc2c7d65fc27 in v15 and newer
versions. This is required on stable branches of v13 and v14 to fix a
regression reported by Noah Misch, introduced by 1f95181b44c8, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints. The backpatched versions of
the patches have been aligned on these branches by me, Noah Misch is the
author. Tests have been conducted by the both of us.
Note that this commit is known to have introduced a regression of its
own. This is fixed by the commit following this one, and not grouped in
a single commit to keep the commit history consistent across all
branches.
Reported-by: Arun Thirupathi
Author: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20210202151416.GB3304930@rfd.leadboat.com
Discussion: https://postgr.es/m/20250306193013.36.nmisch@google.com
Backpatch-through: 13
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Before a restartpoint finishes PreallocXlogFiles(), a startup process
KeepFileRestoredFromArchive() call can unlink the preallocated segment.
If a CHECKPOINT sql command had elicited the restartpoint experiencing
the race condition, that sql command failed. Moreover, the restartpoint
omitted its log_checkpoints message and some inessential resource
reclamation. Prevent the ERROR by skipping open() of the segment.
Since these consequences are so minor, no back-patch.
This commit has been applied as of 2b3e4672f760 in v15 and newer
versions. This is required on stable branches of v13 and v14 to fix a
regression reported by Noah Misch, introduced by 1f95181b44c8, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints. The backpatched versions of
the patches have been aligned on these branches by me, Noah Misch is the
author. Tests have been conducted by the both of us.
Reported-by: Arun Thirupathi
Author: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20210202151416.GB3304930@rfd.leadboat.com
Discussion: https://postgr.es/m/20250306193013.36.nmisch@google.com
Backpatch-through: 13
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This reverts commit 8ad6c5dbbe5a, which was a commit specific to v14 and
older branches as the race condition between restartpoints and
KeepFileRestoredFromArchive() still existed.
1f95181b44c8 has worsened the situation on these two branches, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints. The same logic as v15 and
newer versions will be applied in some follow-up commits to close this
problem, making this HINT not necessary anymore.
Reported-by: Arun Thirupathi
Discussion: https://postgr.es/m/20250306193013.36.nmisch@google.com
Backpatch-through: 13
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Only initdb used it. initdb refuses to operate on a non-empty directory
and generally does not cope with pre-existing files of other kinds.
Hence, use the opportunity to simplify.
This commit has been applied as of 421484f79c0b in v15 and newer
versions. This is required on stable branches of v13 and v14 to fix a
regression reported by Noah Misch, introduced by 1f95181b44c8, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints. The backpatched versions of
the patches have been aligned on these branches by me, Noah Misch is the
author. Tests have been conducted by the both of us.
Reported-by: Arun Thirupathi
Author: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20210202151416.GB3304930@rfd.leadboat.com
Discussion: https://postgr.es/m/20250306193013.36.nmisch@google.com
Backpatch-through: 13
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Infrequently, the mismatch caused log_checkpoints messages and
TRACE_POSTGRESQL_CHECKPOINT_DONE() to witness an "added" count too high
by one. Since that consequence is so minor, no back-patch.
This commit has been applied as of 85656bc3050f in v15 and newer
versions. This is required on stable branches of v13 and v14 to fix a
regression reported by Noah Misch, introduced by 1f95181b44c8, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints. The backpatched versions of
the patches have been aligned on these branches by me, Noah Misch is the
author. Tests have been conducted by the both of us.
Reported-by: Arun Thirupathi
Author: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20210202151416.GB3304930@rfd.leadboat.com
Discussion: https://postgr.es/m/20250306193013.36.nmisch@google.com
Backpatch-through: 13
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Cold paths, initdb and end-of-recovery, used it. Don't optimize them.
This commit has been applied as of c53c6b98d38a in v15 and newer
versions. This is required on stable branches of v13 and v14 to fix a
regression reported by Noah Misch, introduced by 1f95181b44c8, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints. The backpatched versions of
the patches have been aligned on these branches by me, Noah Misch is the
author. Tests have been conducted by the both of us.
Reported-by: Arun Thirupathi
Author: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20210202151416.GB3304930@rfd.leadboat.com
Discussion: https://postgr.es/m/20250306193013.36.nmisch@google.com
Backpatch-through: 13
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XLogPageRead() checks immediately for an invalid WAL record header on a
standby, to be able to handle the case of continuation records that need
to be read across two different sources. As written, the check was too
generic, applying to any target LSN. Based on an analysis by Kyotaro
Horiguchi, what really matters is to make sure that the page header is
checked when attempting to read a LSN at the boundary of a segment, to
handle the case of a continuation record that spawns across multiple
pages when dealing with multiple segments, as WAL receivers are spawned
they request WAL from the beginning of a segment. This fix has been
proposed by Kyotaro Horiguchi.
This could cause standbys to loop infinitely when dealing with a
continuation record during a timeline jump, in the case where the
contents of the record in the follow-up page are invalid.
Some regression tests are added to check such scenarios, able to
reproduce the original problem. In the test, the contents of a
continuation record are overwritten with junk zeros on its follow-up
page, and replayed on standbys. This is inspired by 039_end_of_wal.pl,
and is enough to show how standbys should react on promotion by not
being stuck. Without the fix, the test would fail with a timeout. The
test to reproduce the problem has been written by Alexander Kukushkin.
The original check has been introduced in 066871980183, for a similar
problem.
Author: Kyotaro Horiguchi, Alexander Kukushkin
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/CAFh8B=mozC+e1wGJq0H=0O65goZju+6ab5AU7DEWCSUA2OtwDg@mail.gmail.com
Backpatch-through: 13
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This commit reverts 8f67f994e8ea (down to v13) and c3de0f9eed38 (down to
v17), as these are proving to not be completely correct regarding two
aspects:
- In v17 and newer branches, c3de0f9eed38's check for epoch handling is
incorrect, and does not correctly handle frozen epochs. A logic closer
to widen_snapshot_xid() should be used. The 2PC code should try to
integrate deeper with FullTransactionIds, 5a1dfde8334b being not enough.
- In v13 and newer branches, 8f67f994e8ea is a workaround for the real
issue, which is that we should not attempt CLOG lookups without reaching
consistency. This exists since 728bd991c3c4, and this is reachable with
ProcessTwoPhaseBuffer() called by restoreTwoPhaseData() at the beginning
of recovery.
Per discussion with Noah Misch.
Discussion: https://postgr.es/m/20250116010051.f3.nmisch@google.com
Backpatch-through: 13
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This is a cherry pick of 4c8e00ae from the 14 branch into the 13 branch.
It avoids an assertion failure when ForwardSyncRequest() tries to
allocate memory while trying to compact the queue, if run in a critical
section. RelationTruncate() gained a critical section in 38c579b0, and
could fail in that way in the 13 branch.
b1ffe3ff originally fixed the same problem with TruncateMultiXact(), but
for that case it only needed to go back as far as 14, where SLRUs
started using the sync request queue. It also fixed a related deadlock
risk that doesn't apply in this case (this case doesn't wait), but it
might exist in theory and it doesn't hurt to keep the code the same as
later branches.
Author: Heikki Linnakangas <heikki.linnakangas@iki.fi> (original commit)
Reviewed-by: Michael Paquier <michael@paquier.xyz> (in this new context)
Reported-by: Yura Sokolov <y.sokolov@postgrespro.ru>
Discussion: https://postgr.es/m/f98aaa79-80b5-47c9-832a-31416a3a528b%40postgrespro.ru
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Before 728bd991c3c4, that has improved the support for 2PC files during
recovery, the initial logic scanning files in pg_twophase was done so as
files in the future of the transaction ID horizon were checked first,
followed by a check if a transaction ID is aborted or committed which
could involve a pg_xact lookup. After this commit, these checks have
been done in reverse order.
Files detected as in the future do not have a state that can be checked
in pg_xact, hence this caused recovery to fail abruptly should an
orphaned 2PC file in the future of the transaction ID horizon exist in
pg_twophase at the beginning of recovery.
A test is added to check for this scenario, using an empty 2PC with a
transaction ID large enough to be in the future when running the test.
This test is added in 16 and older versions for now. 17 and newer
versions are impacted by a second bug caused by the addition of the
epoch in the 2PC file names. An equivalent test will be added in these
branches in a follow-up commit, once the second set of issues reported
are fixed.
Author: Vitaly Davydov, Michael Paquier
Discussion: https://postgr.es/m/11e597-676ab680-8d-374f23c0@145466129
Backpatch-through: 13
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Cause parallel workers to not check datallowconn, rolcanlogin, and
ACL_CONNECT privileges. The leader already checked these things
(except for rolcanlogin which might have been checked for a different
role). Re-checking can accomplish little except to induce unexpected
failures in applications that might not even be aware that their query
has been parallelized. We already had the principle that parallel
workers rely on their leader to pass a valid set of authorization
information, so this change just extends that a bit further.
Also, modify the ReservedConnections, datconnlimit and rolconnlimit
logic so that these limits are only enforced against regular backends,
and only regular backends are counted while checking if the limits
were already reached. Previously, background processes that had an
assigned database or role were subject to these limits (with rather
random exclusions for autovac workers and walsenders), and the set of
existing processes that counted against each limit was quite haphazard
as well. The point of these limits, AFAICS, is to ensure the
availability of PGPROC slots for regular backends. Since all other
types of processes have their own separate pools of PGPROC slots, it
makes no sense either to enforce these limits against them or to count
them while enforcing the limit.
While edge-case failures of these sorts have been possible for a
long time, the problem got a good deal worse with commit 5a2fed911
(CVE-2024-10978), which caused parallel workers to make some of these
checks using the leader's current role where before we had used its
AuthenticatedUserId, thus allowing parallel queries to fail after
SET ROLE. The previous behavior was fairly accidental and I have
no desire to return to it.
This patch includes reverting 73c9f91a1, which was an emergency hack
to suppress these same checks in some cases. It wasn't complete,
as shown by a recent bug report from Laurenz Albe. We can also revert
fd4d93d26 and 492217301, which hacked around the same problems in one
regression test.
In passing, remove the special case for autovac workers in
CheckMyDatabase; it seems cleaner to have AutoVacWorkerMain pass
the INIT_PG_OVERRIDE_ALLOW_CONNS flag, now that that does what's
needed.
Like 5a2fed911, back-patch to supported branches (which sadly no
longer includes v12).
Discussion: https://postgr.es/m/1808397.1735156190@sss.pgh.pa.us
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durable_rename_excl() attempts to avoid overwriting any existing files
by using link() and unlink(), and it falls back to rename() on some
platforms (aka WIN32), which offers no such overwrite protection. Most
callers use durable_rename_excl() just in case there is an existing
file, but in practice there shouldn't be one (see below for more
details).
Furthermore, failures during durable_rename_excl() can result in
multiple hard links to the same file. As per Nathan's tests, it is
possible to end up with two links to the same file in pg_wal after a
crash just before unlink() during WAL recycling. Specifically, the test
produced links to the same file for the current WAL file and the next
one because the half-recycled WAL file was re-recycled upon restarting,
leading to WAL corruption.
This change replaces all the calls of durable_rename_excl() to
durable_rename(). This removes the protection against accidentally
overwriting an existing file, but some platforms are already living
without it and ordinarily there shouldn't be one. The function itself
is left around in case any extensions are using it. It will be removed
on HEAD via a follow-up commit.
Here is a summary of the existing callers of durable_rename_excl() (see
second discussion link at the bottom), replaced by this commit. First,
basic_archive used it to avoid overwriting an archive concurrently
created by another server, but as mentioned above, it will still
overwrite files on some platforms. Second, xlog.c uses it to recycle
past WAL segments, where an overwrite should not happen (origin of the
change at f0e37a8) because there are protections about the WAL segment
to select when recycling an entry. The third and last area is related
to the write of timeline history files. writeTimeLineHistory() will
write a new timeline history file at the end of recovery on promotion,
so there should be no such files for the same timeline.
What remains is writeTimeLineHistoryFile(), that can be used in parallel
by a WAL receiver and the startup process, and some digging of the
buildfarm shows that EEXIST from a WAL receiver can happen with an error
of "could not link file \"pg_wal/xlogtemp.NN\" to \"pg_wal/MM.history\",
which would cause an automatic restart of the WAL receiver as it is
promoted to FATAL, hence this should improve the stability of the WAL
receiver as rename() would overwrite an existing TLI history file
already fetched by the startup process at recovery.
This is the second time this change is attempted, ccfbd92 being the
first one, but this time no assertions are added for the case of a TLI
history file written concurrently by the WAL receiver or the startup
process because we can expect one to exist (some of the TAP tests are
able to trigger with a proper timing).
This commit has been originally applied on v16~ as of dac1ff30906b, and
we have received more reports of this issue, where clusters can become
corrupted at replay in older stable branches with multiple links
pointing to the same physical WAL segment file. This backpatch
addresses the problem for the v13~v15 range.
Author: Nathan Bossart
Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/20220407182954.GA1231544@nathanxps13
Discussion: https://postgr.es/m/Ym6GZbqQdlalSKSG@paquier.xyz
Discussion: https://postgr.es/m/CAJhEC04tBkYPF4q2uS_rCytauvNEVqdBAzasBEokfceFhF=KDQ@mail.gmail.com
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This reverts commit d77f91214fb7 on all stable branches, due to concerns
regarding the compatility side effects this could create in a minor
release. The change still exists on HEAD.
Discussion: https://postgr.es/m/CA+TgmoZqRgeFTg4+Yf_CMRRXiHuNz1u6ZC4FvVk+rxw0RmOPnw@mail.gmail.com
Backpatch-through: 13
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When using a pipeline, a transaction starts from the first command and
is committed with a Sync message or when the pipeline ends.
Functions like IsInTransactionBlock() or PreventInTransactionBlock()
were already able to understand a pipeline as being in a transaction
block, but it was not the case of CheckTransactionBlock(). This
function is called for example to generate a WARNING for SET LOCAL,
complaining that it is used outside of a transaction block.
The current state of the code caused multiple problems, like:
- SET LOCAL executed at any stage of a pipeline issued a WARNING, even
if the command was at least second in line where the pipeline is in a
transaction state.
- LOCK TABLE failed when invoked at any step of a pipeline, even if it
should be able to work within a transaction block.
The pipeline protocol assumes that the first command of a pipeline is
not part of a transaction block, and that any follow-up commands is
considered as within a transaction block.
This commit changes the backend so as an implicit transaction block is
started each time the first Execute message of a pipeline has finished
processing, with this implicit transaction block ended once a sync is
processed. The checks based on XACT_FLAGS_PIPELINING in the routines
checking if we are in a transaction block are not necessary: it is
enough to rely on the existing ones.
Some tests are added to pgbench, that can be backpatched down to v17
when \syncpipeline is involved and down to v14 where \startpipeline and
\endpipeline are available. This is unfortunately limited regarding the
error patterns that can be checked, but it provides coverage for various
pipeline combinations to check if these succeed or fail. These tests
are able to capture the case of SET LOCAL's WARNING. The author has
proposed a different feature to improve the coverage by adding similar
meta-commands to psql where error messages could be checked, something
more useful for the cases where commands cannot be used in transaction
blocks, like REINDEX CONCURRENTLY or VACUUM. This is considered as
future work for v18~.
Author: Anthonin Bonnefoy
Reviewed-by: Jelte Fennema-Nio, Michael Paquier
Discussion: https://postgr.es/m/CAO6_XqrWO8uNBQrSu5r6jh+vTGi5Oiyk4y8yXDORdE2jbzw8xw@mail.gmail.com
Backpatch-through: 13
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The SQL spec mandates that SET SESSION AUTHORIZATION implies
SET ROLE NONE. We tried to implement that within the lowest-level
functions that manipulate these settings, but that was a bad idea.
In particular, guc.c assumes that it doesn't matter in what order
it applies GUC variable updates, but that was not the case for these
two variables. This problem, compounded by some hackish attempts to
work around it, led to some security-grade issues:
* Rolling back a transaction that had done SET SESSION AUTHORIZATION
would revert to SET ROLE NONE, even if that had not been the previous
state, so that the effective user ID might now be different from what
it had been.
* The same for SET SESSION AUTHORIZATION in a function SET clause.
* If a parallel worker inspected current_setting('role'), it saw
"none" even when it should see something else.
Also, although the parallel worker startup code intended to cope
with the current role's pg_authid row having disappeared, its
implementation of that was incomplete so it would still fail.
Fix by fully separating the miscinit.c functions that assign
session_authorization from those that assign role. To implement the
spec's requirement, teach set_config_option itself to perform "SET
ROLE NONE" when it sets session_authorization. (This is undoubtedly
ugly, but the alternatives seem worse. In particular, there's no way
to do it within assign_session_authorization without incompatible
changes in the API for GUC assign hooks.) Also, improve
ParallelWorkerMain to directly set all the relevant user-ID variables
instead of relying on some of them to get set indirectly. That
allows us to survive not finding the pg_authid row during worker
startup.
In v16 and earlier, this includes back-patching 9987a7bf3 which
fixed a violation of GUC coding rules: SetSessionAuthorization
is not an appropriate place to be throwing errors from.
Security: CVE-2024-10978
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Commit ac04aa84a put the shutoff for this into the planner, which is
not ideal because it doesn't prevent us from re-using a previously
made parallel plan. Revert the planner change and instead put the
shutoff into InitializeParallelDSM, modeling it on the existing code
there for recovering from failure to allocate a DSM segment.
However, that code path is mostly untested, and testing a bit harder
showed there's at least one bug: ExecHashJoinReInitializeDSM is not
prepared for us to have skipped doing parallel DSM setup. I also
thought the Assert in ReinitializeParallelWorkers is pretty
ill-advised, and replaced it with a silent Min() operation.
The existing test case added by ac04aa84a serves fine to test this
version of the fix, so no change needed there.
Patch by me, but thanks to Noah Misch for the core idea that we
could shut off worker creation when !INTERRUPTS_CAN_BE_PROCESSED.
Back-patch to v12, as ac04aa84a was.
Discussion: https://postgr.es/m/CAC-SaSzHUKT=vZJ8MPxYdC_URPfax+yoA1hKTcF4ROz_Q6z0_Q@mail.gmail.com
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This reverts commit 95c5acb3fc261067ab65ddc0b2dca8e162f09442 (v17) and
counterparts in each other non-master branch. If released, that commit
would have caused a worst-in-years minor release regression, via
undetected LWLock self-deadlock. This commit and its self-deadlock fix
warrant more bake time in the master branch.
Reported by Alexander Lakhin.
Discussion: https://postgr.es/m/10ec0bc3-5933-1189-6bb8-5dec4114558e@gmail.com
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This reverts commit bfd5c6e279c8e1702eea882439dc7ebdf4d4b3a5 (v17) and
counterparts in each other non-master branch. This unblocks reverting a
commit on which it depends.
Discussion: https://postgr.es/m/10ec0bc3-5933-1189-6bb8-5dec4114558e@gmail.com
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A buffer lock won't stop a reader having already checked tuple
visibility. If a vac_update_datfrozenid() and then a crash happened
during inplace update of a relfrozenxid value, datfrozenxid could
overtake relfrozenxid. That could lead to "could not access status of
transaction" errors. Back-patch to v12 (all supported versions). In
v14 and earlier, this also back-patches the assertion removal from
commit 7fcf2faf9c7dd473208fd6d5565f88d7f733782b.
Discussion: https://postgr.es/m/20240620012908.92.nmisch@google.com
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The inplace update survives ROLLBACK. The inval didn't, so another
backend's DDL could then update the row without incorporating the
inplace update. In the test this fixes, a mix of CREATE INDEX and ALTER
TABLE resulted in a table with an index, yet relhasindex=f. That is a
source of index corruption. Back-patch to v12 (all supported versions).
The back branch versions don't change WAL, because those branches just
added end-of-recovery SIResetAll(). All branches change the ABI of
extern function PrepareToInvalidateCacheTuple(). No PGXN extension
calls that, and there's no apparent use case in extensions.
Reviewed by Nitin Motiani and (in earlier versions) Andres Freund.
Discussion: https://postgr.es/m/20240523000548.58.nmisch@google.com
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An inplace update's invalidation messages are part of its transaction's
commit record. However, the update survives even if its transaction
aborts or we stop recovery before replaying its transaction commit.
After recovery, a backend that started in recovery could update the row
without incorporating the inplace update. That could result in a table
with an index, yet relhasindex=f. That is a source of index corruption.
This bulk invalidation avoids the functional consequences. A future
change can fix the !RecoveryInProgress() scenario without changing the
WAL format. Back-patch to v17 - v12 (all supported versions). v18 will
instead add invalidations to WAL.
Discussion: https://postgr.es/m/20240618152349.7f.nmisch@google.com
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COMMIT PREPARED removes on-disk 2PC files near its end, but the state
checked if a file is on-disk or not gets read from shared memory while
not holding the two-phase state lock.
Because of that, there was a small window where a second backend doing a
PREPARE TRANSACTION could reuse the GlobalTransaction put back into the
2PC free list by the COMMIT PREPARED, overwriting the "ondisk" flag read
afterwards by the COMMIT PREPARED to decide if its on-disk two-phase
state file should be removed, preventing the file deletion.
This commit fixes this issue so as the "ondisk" flag in the
GlobalTransaction is read while holding the two-phase state lock, not
from shared memory after its entry has been added to the free list.
Orphaned two-phase state files flushed to disk after a checkpoint are
discarded at the beginning of recovery. However, a truncation of
pg_xact/ would make the startup process issue a FATAL when it cannot
read the SLRU page holding the state of the transaction whose 2PC file
was orphaned, which is a necessary step to decide if the 2PC file should
be removed or not. Removing manually the file would be necessary in
this case.
Issue introduced by effe7d9552dd, so backpatch all the way down.
Mea culpa.
Author: wuchengwen
Discussion: https://postgr.es/m/tencent_A7F059B5136A359625C7B2E4A386B3C3F007@qq.com
Backpatch-through: 12
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This reverts commit 216201027d90e99a0a2b2d2efba85dc0aac94c62.
Some buildfarm animals are failing with "cannot change
"client_encoding" during a parallel operation". It looks like
assign_client_encoding is unhappy at being asked to roll back a
client_encoding setting after a parallel worker encounters a
failure. There must be more to it though: why didn't I see this
during local testing? In any case, it's clear that moving the
RestoreGUCState() call is not as side-effect-free as I thought.
Given that the bug f5f30c22e intended to fix has gone unreported
for years, it's not something that's urgent to fix; I'm not
willing to risk messing with it further with only days to our
next release wrap.
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Parallel workers failed after a sequence like
BEGIN;
CREATE USER foo;
SET SESSION AUTHORIZATION foo;
because check_session_authorization could not see the uncommitted
pg_authid row for "foo". This is because we ran RestoreGUCState()
in a separate transaction using an ordinary just-created snapshot.
The same disease afflicts any other GUC that requires catalog lookups
and isn't forgiving about the lookups failing.
To fix, postpone RestoreGUCState() into the worker's main transaction
after we've set up a snapshot duplicating the leader's. This affects
check_transaction_isolation and check_transaction_deferrable, which
think they should only run during transaction start. Make them
act like check_transaction_read_only, which already knows it should
silently accept the value when InitializingParallelWorker.
Per bug #18545 from Andrey Rachitskiy. Back-patch to all
supported branches, because this has been wrong for awhile.
Discussion: https://postgr.es/m/18545-feba138862f19aaa@postgresql.org
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We did not recover the subtransaction IDs of prepared transactions
when starting a hot standby from a shutdown checkpoint. As a result,
such subtransactions were considered as aborted, rather than
in-progress. That would lead to hint bits being set incorrectly, and
the subtransactions suddenly becoming visible to old snapshots when
the prepared transaction was committed.
To fix, update pg_subtrans with prepared transactions's subxids when
starting hot standby from a shutdown checkpoint. The snapshots taken
from that state need to be marked as "suboverflowed", so that we also
check the pg_subtrans.
Backport to all supported versions.
Discussion: https://www.postgresql.org/message-id/6b852e98-2d49-4ca1-9e95-db419a2696e0@iki.fi
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The purpose of the function is to reduce the effective
autovacuum_multixact_freeze_max_age if the multixact members SLRU is
approaching wraparound, to make multixid freezing more aggressive.
The returned value should therefore never be greater than plain
autovacuum_multixact_freeze_max_age.
Reviewed-by: Robert Haas
Discussion: https://www.postgresql.org/message-id/85fb354c-f89f-4d47-b3a2-3cbd461c90a3@iki.fi
Backpatch-through: 12, all supported versions
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Until now LWLockDequeueSelf() sequentially searched the list of waiters to see
if the current proc is still is on the list of waiters, or has already been
removed. In extreme workloads, where the wait lists are very long, this leads
to a quadratic behavior. #backends iterating over a list #backends
long. Additionally, the likelihood of needing to call LWLockDequeueSelf() in
the first place also increases with the increased length of the wait queue, as
it becomes more likely that a lock is released while waiting for the wait list
lock, which is held for longer during lock release.
Due to the exponential back-off in perform_spin_delay() this is surprisingly
hard to detect. We should make that easier, e.g. by adding a wait event around
the pg_usleep() - but that's a separate patch.
The fix is simple - track whether a proc is currently waiting in the wait list
or already removed but waiting to be woken up in PGPROC->lwWaiting.
In some workloads with a lot of clients contending for a small number of
lwlocks (e.g. WALWriteLock), the fix can substantially increase throughput.
This has been originally fixed for 16~ with a4adc31f6902 without a
backpatch, and we have heard complaints from users impacted by this
quadratic behavior in older versions as well.
Author: Andres Freund <andres@anarazel.de>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/20221027165914.2hofzp4cvutj6gin@awork3.anarazel.de
Discussion: https://postgr.es/m/CALj2ACXktNbG=K8Xi7PSqbofTZozavhaxjatVc14iYaLu4Maag@mail.gmail.com
Backpatch-through: 12
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Dead tuples are ignored and are not marked as dead during recovery, as
it can lead to MVCC issues on a standby because its xmin may not match
with the primary. This information is tracked by a field called
"xactStartedInRecovery" in the transaction state data, switched on when
starting a transaction in recovery.
Unfortunately, this information was not correctly tracked when starting
a subtransaction, because the transaction state used for the
subtransaction did not update "xactStartedInRecovery" based on the state
of its parent. This would cause index scans done in subtransactions to
return inconsistent data, depending on how the xmin of the primary
and/or the standby evolved.
This is broken since the introduction of hot standby in efc16ea52067, so
backpatch all the way down.
Author: Fei Changhong
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/tencent_C4D907A5093C071A029712E73B43C6512706@qq.com
Backpatch-through: 12
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This has been broken since b060dbe0001a that has reworked the callback
mechanism of XLogReader, most likely unnoticed because any form of
development involving WAL happens on platforms where this compiles fine.
Author: Bharath Rupireddy
Discussion: https://postgr.es/m/CALj2ACVF14WKQMFwcJ=3okVDhiXpuK5f7YdT+BdYXbbypMHqWA@mail.gmail.com
Backpatch-through: 13
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Mark the buffers dirty before writing WAL.
Discussion: https://postgr.es/m/25104133-7df8-cae3-b9a2-1c0aaa1c094a@iki.fi
Reviewed-by: Heikki Linnakangas
Backpatch-through: 11
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This commit changes the WAL reader routines so as a FATAL for the
backend or exit(FAILURE) for the frontend is triggered if an allocation
for a WAL record decode fails in walreader.c, rather than treating this
case as bogus data, which would be equivalent to the end of WAL. The
key is to avoid palloc_extended(MCXT_ALLOC_NO_OOM) in walreader.c,
relying on plain palloc() calls.
The previous behavior could make WAL replay finish too early than it
should. For example, crash recovery finishing earlier may corrupt
clusters because not all the WAL available locally was replayed to
ensure a consistent state. Out-of-memory failures would show up
randomly depending on the memory pressure on the host, but one simple
case would be to generate a large record, then replay this record after
downsizing a host, as Ethan Mertz originally reported.
This relies on bae868caf222, as the WAL reader routines now do the
memory allocation required for a record only once its header has been
fully read and validated, making xl_tot_len trustable. Making the WAL
reader react differently on out-of-memory or bogus record data would
require ABI changes, so this is the safest choice for stable branches.
Also, it is worth noting that 3f1ce973467a has been using a plain
palloc() in this code for some time now.
Thanks to Noah Misch and Thomas Munro for the discussion.
Like the other commit, backpatch down to 12, leaving out v11 that will
be EOL'd soon. The behavior of considering a failed allocation as bogus
data comes originally from 0ffe11abd3a0, where the record length
retrieved from its header was not entirely trustable.
Reported-by: Ethan Mertz
Discussion: https://postgr.es/m/ZRKKdI5-RRlta3aF@paquier.xyz
Backpatch-through: 12
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bae868ca removed a check that was still needed. If you had an
xl_tot_len at the end of a page that was too small for a record header,
but not big enough to span onto the next page, we'd immediately perform
the CRC check using a bogus large length. Because of arbitrary coding
differences between the CRC implementations on different platforms,
nothing very bad happened on common modern systems. On systems using
the _sb8.c fallback we could segfault.
Restore that check, add a new assertion and supply a test for that case.
Back-patch to 12, like bae868ca.
Tested-by: Tom Lane <tgl@sss.pgh.pa.us>
Tested-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGLCkTT7zYjzOxuLGahBdQ%3DMcF%3Dz5ZvrjSOnW4EDhVjT-g%40mail.gmail.com
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xl_tot_len comes first in a WAL record. Usually we don't trust it to be
the true length until we've validated the record header. If the record
header was split across two pages, previously we wouldn't do the
validation until after we'd already tried to allocate enough memory to
hold the record, which was bad because it might actually be garbage
bytes from a recycled WAL file, so we could try to allocate a lot of
memory. Release 15 made it worse.
Since 70b4f82a4b5, we'd at least generate an end-of-WAL condition if the
garbage 4 byte value happened to be > 1GB, but we'd still try to
allocate up to 1GB of memory bogusly otherwise. That was an
improvement, but unfortunately release 15 tries to allocate another
object before that, so you could get a FATAL error and recovery could
fail.
We can fix both variants of the problem more fundamentally using
pre-existing page-level validation, if we just re-order some logic.
The new order of operations in the split-header case defers all memory
allocation based on xl_tot_len until we've read the following page. At
that point we know that its first few bytes are not recycled data, by
checking its xlp_pageaddr, and that its xlp_rem_len agrees with
xl_tot_len on the preceding page. That is strong evidence that
xl_tot_len was truly the start of a record that was logged.
This problem was most likely to occur on a standby, because
walreceiver.c recycles WAL files without zeroing out trailing regions of
each page. We could fix that too, but it wouldn't protect us from rare
crash scenarios where the trailing zeroes don't make it to disk.
With reliable xl_tot_len validation in place, the ancient policy of
considering malloc failure to indicate corruption at end-of-WAL seems
quite surprising, but changing that is left for later work.
Also included is a new TAP test to exercise various cases of end-of-WAL
detection by writing contrived data into the WAL from Perl.
Back-patch to 12. We decided not to put this change into the final
release of 11.
Author: Thomas Munro <thomas.munro@gmail.com>
Author: Michael Paquier <michael@paquier.xyz>
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Reviewed-by: Noah Misch <noah@leadboat.com> (the idea, not the code)
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Sergei Kornilov <sk@zsrv.org>
Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/17928-aa92416a70ff44a2%40postgresql.org
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In older branches, COMMIT/ROLLBACK AND CHAIN failed to propagate
the current transaction's properties to the new transaction if
there was any open subtransaction (unreleased savepoint).
Instead, some previous transaction's properties would be restored.
This is because the "if (s->chain)" check in CommitTransactionCommand
examined the wrong instance of the "chain" flag and falsely
concluded that it didn't need to save transaction properties.
Our regression tests would have noticed this, except they used
identical transaction properties for multiple tests in a row,
so that the faulty behavior was not distinguishable from correct
behavior.
Commit 12d768e70 fixed the problem in v15 and later, but only rather
accidentally, because I removed the "if (s->chain)" test to avoid a
compiler warning, while not realizing that the warning was flagging a
real bug.
In v14 and before, remove the if-test and save transaction properties
unconditionally; just as in the newer branches, that's not expensive
enough to justify thinking harder.
Add the comment and extra regression test to v15 and later to
forestall any future recurrence, but there's no live bug in those
branches.
Patch by me, per bug #18118 from Liu Xiang. Back-patch to v12 where
the AND CHAIN feature was added.
Discussion: https://postgr.es/m/18118-4b72fcbb903aace6@postgresql.org
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Commit 0668719801 changed XLogPageRead() so that it validated the page
header, if invalid page header was found reset the error message and
retried reading the page, to fix the scenario where streaming standby
got stuck at a continuation record. This change hid the error message
about invalid page header, which would make it harder for users to
investigate what the actual issue was found in WAL.
To fix the issue, this commit makes XLogPageRead() report the error
message when invalid page header is found.
When not in standby mode, an invalid page header should cause recovery
to end, not retry reading the page, so XLogPageRead() doesn't need to
validate the page header for the retry. Instead, ReadPageInternal() should
be responsible for the validation in that case. Therefore this commit
changes XLogPageRead() so that if not in standby mode it doesn't validate
the page header for the retry.
This commit has been originally pushed as of 68601985e699 for 15 and
newer versions, but not to the older branches. A recent investigation
related to WAL replay failures has showed up that the lack of this patch
in 12~14 is an issue, as we want to be able to improve the WAL reader to
make a correct distinction between the end-of-wal and OOM cases when
validating record headers. REL_11_STABLE is left out as it will be
EOL'd soon.
Reported-by: Yugo Nagata
Author: Yugo Nagata, Kyotaro Horiguchi
Reviewed-by: Ranier Vilela, Fujii Masao
Discussion: https://postgr.es/m/20210718045505.32f463ed6c227111038d8ae4@sraoss.co.jp
Discussion: https://postgr.es/m/17928-aa92416a70ff44a2@postgresql.org
Backpatch-through: 12
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This has been missed in cb0cca1, noticed before buildfarm member koel
has been able to complain while poking at a different patch. Like the
other commit, backpatch all the way down to limit the odds of merge
conflicts.
Backpatch-through: 11
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A crash in the middle of a checkpoint with some two-phase state data
already flushed to disk by this checkpoint could cause a follow-up crash
recovery to recover twice the same transaction, once from what has been
found in pg_twophase/ at the beginning of recovery and a second time
when replaying its corresponding record.
This would lead to FATAL failures in the startup process during
recovery, where the same transaction would have a state recovered twice
instead of once:
LOG: recovering prepared transaction 731 from shared memory
LOG: recovering prepared transaction 731 from shared memory
FATAL: lock ExclusiveLock on object 731/0/0 is already held
This issue is fixed by skipping the addition of any 2PC state coming
from a record whose equivalent 2PC state file has already been loaded in
TwoPhaseState at the beginning of recovery by restoreTwoPhaseData(),
which is OK as long as the system has not reached a consistent state.
The timing to get a messed up recovery processing is very racy, and
would very unlikely happen. The thread that has reported the issue has
demonstrated the bug using injection points to force a PANIC in the
middle of a checkpoint.
Issue introduced in 728bd99, so backpatch all the way down.
Reported-by: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>
Author: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>
Author: Michael Paquier
Discussion: https://postgr.es/m/109e6994-b971-48cb-84f6-829646f18b4c.mengjuan.cmj@alibaba-inc.com
Backpatch-through: 11
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This is a follow-up of f663b00, that has been committed to v13 and v14,
tweaking the TAP test for two-phase transactions so as it provides
coverage for the bug that has been fixed. This change is done in its
own commit for clarity, as v15 and HEAD did not show the problematic
behavior, still missed coverage for it.
While on it, this adds a comment about the dependency of the last
partial segment rename and RecoverPreparedTransactions() at the end of
recovery, as that can be easy to miss.
Author: Michael Paquier
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/743b9b45a2d4013bd90b6a5cba8d6faeb717ee34.camel@cybertec.at
Backpatch-through: 13
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When archiving is enabled, a promotion request would fail with the
following error when some 2PC transaction needs to be recovered from
WAL, preventing the promotion to complete:
FATAL: requested WAL segment pg_wal/000000010000000000000001 has already been removed
The origin of the problem is that the last partial segment of the old
timeline is renamed before recovering the 2PC data via
RecoverPreparedTransactions() at the end of recovery, causing the FATAL
because the segment wanted is now renamed with a .partial suffix. This
commit reorders a bit the end-of-recovery actions so as the execution of
recovery_end_command, the cleanup of the old segments of the old
timeline (RemoveNonParentXlogFiles) and the last partial segment rename
are done after the 2PC transaction data is recovered with
RecoverPreparedTransactions(). This makes the order of these
end-of-recovery actions more consistent with ~15, at the exception of
the end-of-recovery checkpoint that still needs to happen before all the
actions reordered here in v13 and v14, contrary to what 15~ does.
v15 and newer versions have "fixed" this problem somewhat accidentally
with 811051c, where the end-of-recovery actions got reordered. In this
case, the recovery of 2PC transactions happens before the renaming of
the last partial segment of the old timeline.
v13 and v14 are the versions that can easily see this problem as per the
refactoring of 38a95731 where XLogReaderState is reset in
XLogBeginRead() before reading the 2PC transaction data. v11 and v12
could also see this problem, but may finish by reading the 2PC data from
some of the WAL buffers instead. Perhaps something could be done for
these two branches, but I am not really excited about doing something on
these per the lack of complaints and per the fact that v11 is soon going
to be EOL'd soon (there is always a risk of breaking something).
Note that the TAP test 009_twophase.pl is able to exhibit the issue if
it enables archiving on the primary node, which does not impact the test
coverage as restore_command would remain unused. This is something that
should be changed on v15 and HEAD as well, so this will be changed in a
separate commit for clarity.
Author: Julian Markwort
Reviewed-by: Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/743b9b45a2d4013bd90b6a5cba8d6faeb717ee34.camel@cybertec.at
Backpatch-through: 13
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In reality, recordXtime will always be set by the getRecordTimestamp
call, but the compiler doesn't necessarily see that.
Back-patch to all supported versions.
Author: Tristan Partin
Discussion: https://www.postgresql.org/message-id/CT5MN8E11U0M.1NYNCHXYUHY41@gonk
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The call to XLogGetReplicationSlotMinimumLSN() might return a
greater LSN than the one given to the function. Subsequent segment
number calculations might then underflow, which could result in
unexpected behavior when removing or recyling WAL files. This was
introduced with max_slot_wal_keep_size in c655077639. To fix, skip
the block of code for replication slots if the LSN is greater.
Reported-by: Xu Xingwang
Author: Kyotaro Horiguchi
Reviewed-by: Junwang Zhao
Discussion: https://postgr.es/m/17903-4288d439dee856c6%40postgresql.org
Backpatch-through: 13
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If the last few pages in the specified range are empty (all zero),
then log_newpage_range() could try to emit an empty WAL record
containing no FPIs. This at least upsets an Assert in
ReserveXLogInsertLocation, and might perhaps have bad real-world
consequences in non-assert builds.
This has been broken since log_newpage_range() was introduced,
but the case was hard if not impossible to hit before commit 3d6a98457
decided it was okay to leave VM and FSM pages intentionally zero.
Nonetheless, it seems prudent to back-patch. log_newpage_range()
was added in v12 but later back-patched, so this affects all
supported branches.
Matthias van de Meent, per report from Justin Pryzby
Discussion: https://postgr.es/m/ZD1daibg4RF50IOj@telsasoft.com
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When ending recovery based on recovery_target_xid matching with
recovery_target_inclusive = off, we printed an incorrect timestamp
(always 2000-01-01) in the "recovery stopping before ... transaction"
log message. This is a consequence of sloppy refactoring in
c945af80c: the code to fetch recordXtime out of the commit/abort
record used to be executed unconditionally, but it was changed
to get called only in the RECOVERY_TARGET_TIME case. We need only
flip the order of operations to restore the intended behavior.
Per report from Torsten Förtsch. Back-patch to all supported
branches.
Discussion: https://postgr.es/m/CAKkG4_kUevPqbmyOfLajx7opAQk6Cvwkvx0HRcFjSPfRPTXanA@mail.gmail.com
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Commits f92944137 et al. made IsInTransactionBlock() set the
XACT_FLAGS_NEEDIMMEDIATECOMMIT flag before returning "false",
on the grounds that that kept its API promises equivalent to those of
PreventInTransactionBlock(). This turns out to be a bad idea though,
because it allows an ANALYZE in a pipelined series of commands to
cause an immediate commit, which is unexpected.
Furthermore, if we return "false" then we have another issue,
which is that ANALYZE will decide it's allowed to do internal
commit-and-start-transaction sequences, thus possibly unexpectedly
committing the effects of previous commands in the pipeline.
To fix the latter situation, invent another transaction state flag
XACT_FLAGS_PIPELINING, which explicitly records the fact that we
have executed some extended-protocol command and not yet seen a
commit for it. Then, require that flag to not be set before allowing
InTransactionBlock() to return "false".
Having done that, we can remove its setting of NEEDIMMEDIATECOMMIT
without fear of causing problems. This means that the API guarantees
of IsInTransactionBlock now diverge from PreventInTransactionBlock,
which is mildly annoying, but it seems OK given the very limited usage
of IsInTransactionBlock. (In any case, a caller preferring the old
behavior could always set NEEDIMMEDIATECOMMIT for itself.)
For consistency also require XACT_FLAGS_PIPELINING to not be set
in PreventInTransactionBlock. This too is meant to prevent commands
such as CREATE DATABASE from silently committing previous commands
in a pipeline.
Per report from Peter Eisentraut. As before, back-patch to all
supported branches (which sadly no longer includes v10).
Discussion: https://postgr.es/m/65a899dd-aebc-f667-1d0a-abb89ff3abf8@enterprisedb.com
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Previously, we'd compress only when the active range of array entries
reached Max(4 * PROCARRAY_MAXPROCS, 2 * pArray->numKnownAssignedXids).
If max_connections is large, the first term could result in not
compressing for a long time, resulting in much wastage of cycles in
hot-standby backends scanning the array to take snapshots. Get rid
of that term, and just bound it to 2 * pArray->numKnownAssignedXids.
That however creates the opposite risk, that we might spend too much
effort compressing. Hence, consider compressing only once every 128
commit records. (This frequency was chosen by benchmarking. While
we only tried one benchmark scenario, the results seem stable over
a fairly wide range of frequencies.)
Also, force compression when processing RecoveryInfo WAL records
(which should be infrequent); the old code could perform compression
then, but would do so only after the same array-range check as for
the transaction-commit path.
Also, opportunistically run compression if the startup process is about
to wait for WAL, though not oftener than once a second. This should
prevent cases where we waste lots of time by leaving the array
not-compressed for long intervals due to low WAL traffic.
Lastly, add a simple check to keep us from uselessly compressing
when the array storage is already compact.
Back-patch, as the performance problem is worse in pre-v14 branches
than in HEAD.
Simon Riggs and Michail Nikolaev, with help from Tom Lane and
Andres Freund.
Discussion: https://postgr.es/m/CALdSSPgahNUD_=pB_j=1zSnDBaiOtqVfzo8Ejt5J_k7qZiU1Tw@mail.gmail.com
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There are recent reports involving a very old error message that we have
no history of hitting -- perhaps a recently introduced bug. Improve the
error message in an attempt to improve our chances of investigating the
bug.
Per reports from Dimos Stamatakis and Bob Krier.
Backpatch to 11.
Discussion: https://postgr.es/m/CO2PR0801MB2310579F65529380A4E5EDC0E20A9@CO2PR0801MB2310.namprd08.prod.outlook.com
Discussion: https://postgr.es/m/17518-04e368df5ad7f2ee@postgresql.org
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Add a little to the header comments for these functions to make it
clearer what guarantees about commit behavior are provided to callers.
(See commit f92944137 for context.)
Although this is only a comment change, it's really documentation
aimed at authors of extensions, so it seems appropriate to back-patch.
Yugo Nagata and Tom Lane, per further discussion of bug #17434.
Discussion: https://postgr.es/m/17434-d9f7a064ce2a88a3@postgresql.org
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clang 15+ will issue a set-but-not-used warning when the only
use of a variable is in autoincrements (e.g., "foo++;").
That's perfectly sensible, but it detects a few more cases that
we'd not noticed before. Silence the warnings with our usual
methods, such as PG_USED_FOR_ASSERTS_ONLY, or in one case by
actually removing a useless variable.
One thing that we can't nicely get rid of is that with %pure-parser,
Bison emits "yynerrs" as a local variable that falls foul of this
warning. To silence those, I inserted "(void) yynerrs;" in the
top-level productions of affected grammars.
Per recently-established project policy, this is a candidate
for back-patching into out-of-support branches: it suppresses
annoying compiler warnings but changes no behavior. Hence,
back-patch to 9.5, which is as far as these patches go without
issues. (A preliminary check shows that the prior branches
need some other set-but-not-used cleanups too, so I'll leave
them for another day.)
Discussion: https://postgr.es/m/514615.1663615243@sss.pgh.pa.us
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When a PostgreSQL instance performing archive recovery but not using
standby mode is promoted, and the last WAL segment that it attempted
to read ended in a partial record, the previous code would create
invalid WAL on the new timeline. The WAL from the previously timeline
would be copied to the new timeline up until the end of the last valid
record, but instead of beginning to write WAL at immediately
afterwards, the promoted server would write an overwrite contrecord at
the beginning of the next segment. The end of the previous segment
would be left as all-zeroes, resulting in failures if anything tried
to read WAL from that file.
The root of the issue is that ReadRecord() decides whether to set
abortedRecPtr and missingContrecPtr based on the value of StandbyMode,
but ReadRecord() switches to a new timeline based on the value of
ArchiveRecoveryRequested. We shouldn't try to write an overwrite
contrecord if we're switching to a new timeline, so change the test in
ReadRecod() to check ArchiveRecoveryRequested instead.
Code fix by Dilip Kumar. Comments by me incorporating suggested
language from Álvaro Herrera. Further review from Kyotaro Horiguchi
and Sami Imseih.
Discussion: http://postgr.es/m/CAFiTN-t7umki=PK8dT1tcPV=mOUe2vNhHML6b3T7W7qqvvajjg@mail.gmail.com
Discussion: http://postgr.es/m/FB0DEA0B-E14E-43A0-811F-C1AE93D00FF3%40amazon.com
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